Uric Acid Metabolism in Elderly Patients

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We studied uric acid metabolism in elderly patients, in order to determine the effect of decreased muscular exercise relative to purine metabolism. We also investigated by means of oral inosine loading wheter there was any defect either in the production or renal excretion of uric acid in each patient.<BR>Seventy-eight patients(males 28,77.3±6.1years old and females 50,79.2±5.7 years old)were divided into three groups according to basic activity level in daily living; the first group was composed of 26 bedridden patients, the second of 14 who could only move and take care of themselves with instrumental supports, and the third of 38 who could maintain a voluntary life style. Each subject in the patient group was receiving medication for arteriosclerotic disease. However, most of these medication have no significant effects on urate metabolism in humans.<BR>After ultrasonographic measurement of upper arm skinfold thickness, muscle volume (MV)was calculated according to Heymsfield et al. We carried out a 24-hr urate clearance study and oral inosine loading for three days in five bedridden patients. The mass of MV showed a significant negative correlation with the increase in age of the patient. Serum uric acid ( s-UA) levels were distributed among the patient group between 1.5 and 6.9mg/d<I>l</I>, and five females of the patient group showed levels below 2.0mg/d<I>l</I>. Urate output from the patient group was as low as 97.9±115.2. mg/day. There was a positive correlation between the mass of MV and s-UA levels in the patient group. S-UA levels, in the patients of the third group who were maintaining an active life style, were signifcantly higher than those of the bedridden patients. S-UA levels in the five patients of the first group increased signifcantly from 3.5±1.8 to 7.7±2.3mg/d<I>l</I> after oral inosine loading. Urate output and urate clearance also increased after loading, although there were no significant changes in creatinine clearance in these patients.<BR>It is known that muscular exercise increases purine metabolism due to enhanced ATP consumption and results in hyperuricemia, and that hyperuricemia and gouty attacks are frequently found in most sportsmen. However, there are few studies concerning the decreased production of uric acid under decreased muscular exercise.<BR>The present studies suggests that in elderly subjects the turn-over of purine metabolism is decreased, because of the reduction of muscle volume and muscular exercise, resulting in lower levels of serum uric acid and urate output in elderly patients. There was no impairment in the metabolic process from inosine to uric acid, nor in the renal excretory mechanism of uric acid.
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